May16-18, 2017 Warsaw, Poland 8 TH CONFERENCE ON SEVERE ACCIDENT RESEARCH ERMSAR 2017 MC3D Premixing Analysis using X-Ray Radioscopy Experimental Data of KROTOS-SERENA Tests M. Leskovar a , V. Centrih a , M. Uršič a , N. Cassiaut Louis b , C. Brayer b , P. Piluso b a Jožef Stefan Institute, Ljubljana, Slovenia b CEA Cadarache, France
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May16-18, 2017
Warsaw, Poland
8TH CONFERENCE
ON SEVERE ACCIDENT
RESEARCH
ERMSAR 2017
MC3D Premixing Analysis using X-Ray
Radioscopy Experimental Data
of KROTOS-SERENA Tests
M. Leskovara, V. Centriha, M. Uršiča,
N. Cassiaut Louisb, C. Brayerb, P. Pilusob
aJožef Stefan Institute, Ljubljana, Slovenia
bCEA Cadarache, France
ERMSAR 2017, Warsaw, May 16-18, 2017
Outline
• Introduction
• Experimental observations
• KROTOS-SERENA X-ray radioscopy experimental data
• New insights for MC3D modelling
• MC3D premixing simulations
• Melt jet release and breakup modelling
• Lateral premixture extension analysis
• Conclusions
2
ERMSAR 2017, Warsaw, May 16-18, 2017
Introduction
• Steam explosion
• During a severe accident, molten core may be released from failed reactor vessel into flooded
reactor cavity → Fuel-Coolant Interaction (FCI)
• Important condition for possible steam explosion is premixture formation
• OECD SERENA Phase 2 project
• Experimental and analytical part
• 12 complementary tests in KROTOS (CEA) and TROI (KAERI) facilities
• 6 KROTOS-SERENA (KS) tests performed (KFC, KS-1 to KS-6)
• Goal: Improving understanding and modelling of FCI processes, increasing the capabilities of FCI
models/codes for use in reactor analyses
• Comprehensive report on KROTOS X-ray data analysis by CEA:
• KROTOS Radioscopy Data Analysis for KFC Test and KS-Series Tests, N. Cassiaut-Louis & D.
Grishchenko, 2016
• Objective of the work: Improve understanding and modelling of premixing processes based on X-ray data
3
ERMSAR 2017, Warsaw, May 16-18, 2017
KROTOS KS Experimental Data
• KROTOS experimental facility – melt poured into water pool
4
KFC KS-1 KS-2 KS-4
Water level
Water depth
0.00 m
0.15 m
0.30 m
0.45 m
0.60 m
KS-5
KS-6
Water: 1145 mm
• Pressure transducers, Video
camera, Pyrometer, Water level
transducer, Thermocouples -
water temperature, Sacrificial
thermocouples - detection of
melt propagation
• X-ray radioscopy (200 x 300 mm
window) – position varied
ERMSAR 2017, Warsaw, May 16-18, 2017
KROTOS KS X-Ray Data
• KROTOS radioscopy data analysis
• X-ray images analysed and post-processed (KIWI software, CEA)
• Qualitative and quantitative data for corium and void obtained
• Results of image analysis:
1. Corium volume and surface area per fragment
2. Cumulative corium volume in the premixture
3. Velocity of corium fragments and jet characteristic points
4. Void volume and surface area
5. Void volume distribution in Cartesian and axisymmetric
cylindrical coordinates (provided only at triggering time)
• Important for our MC3D (IRSN) analysis:
• Evolution of corium passing through X-ray window
• Evolution of void volume and fraction within X-ray window
• Void volume distribution at triggering time
5
Post-processed:
Void
Post-processed:
Melt & Void
ERMSAR 2017, Warsaw, May 16-18, 2017
Experimental Observations - Corium
• Experimental data for melt jet release determination
• Sacrificial thermocouples
• X-ray corium data: KFC and KS-1 test
Image position near water level – not so complex premixing
Better estimation of mass flow rate
• Cumulative delivered mass (X-ray corium data in diagrams)
6
0
0,5
1
1,5
2
0 0,1 0,2 0,3 0,4 0,5 0,6 0,7
Cum
ula
tive
co
riu
m m
ass
[kg
]
Time [s]
Total
Inframe
Below
KFC
0
0,5
1
1,5
2
0 0,1 0,2 0,3 0,4 0,5 0,6 0,7
Cum
ula
tive
co
riu
m m
ass
[kg
]
Time [s]
Total
InFrame
Below
KS1
KFC KS-1 KS-2 KS-4
Water level
Water depth
0.00 m
0.15 m
0.30 m
0.45 m
0.60 m
KS-5
KS-6
Water: 1145 mm
• KFC test
No fusible disc → fast initial
droplet spray
• KS-1 test
Fusible disc → suspended
melt release, gravity pour
Slope → melt mass flow rate
ERMSAR 2017, Warsaw, May 16-18, 2017
Experimental Observations - Corium
• Three main melt jet parameters may be revised based on X-ray corium data analysis
1. Melt mass flow rate
From jet diameter & velocity at water level → 4.4 kg/s
Slope of KS-1 cumulative corium evolution → 3.6 kg/s Slight under-prediction expected (smallest droplets not seen)
Estimation ~ 4.0 kg/s
2. Jet impact velocity
From thermocouples: all tests 3.3 to 4.1 m/s KS-1 → 3.6 m/s
KS-4 → 3.3 m/s (additional guide tube)
X-ray data: KS-1 → 3.6 m/s
3. Jet breakup length
From thermocouples: 35 – 46 cm
From X-ray images: 25 – 30 cm
7
KS1 rate = 3,6135
KFC rate1 = 6,7601
KFC rate2 = 2,2374
0,0
0,5
1,0
1,5
2,0
0,2 0,4 0,6 0,8 1 1,2
Cu
mu
lati
ve c
ori
um
mas
s [k
g]
Time [s]
KS1
KFC
KS1 rate
KFC rate1
KFC rate2
ERMSAR 2017, Warsaw, May 16-18, 2017
MC3D Modelling
• MC3D (IRSN) mesh and calculation conditions
• Only premixing phase simulated
• KS-4 test conditions applied
8
Corium
Water
Calc. mesh20 x 120 cells
MC3D v3.8
KS-4 x-rayframeposition
Experimental KS-4 conditions
Initial melt temperature 2963 K
Melt mass 3.2 kg
Water temperature 333 K
Ambient pressure 0.21 MPa
Sub-cooling 60 K
Material properties
80% UO2 / 20% ZrO2 Near eutectic
Liquidus/solidus temperature 2920 K / 2870 K
Latent heat 280 kJ/kg
Specific heat (liquidus/solidus) 510 / 450 J/kg∙K
Density 6866 kg/m3
MC3D modelling conditions
Jet fragmentation model Global model
Fragmentation rate coefficient 0.075 m3/m2/s
Sauter diameter 2.5 mm
Release nozzle diameter, exp. / sim. 30 mm / 25 mm
Calculation time 2 s
Release nozzle
ERMSAR 2017, Warsaw, May 16-18, 2017
Premixing Modelling – Melt Jet Release
• Mass flow rate
• May be adjusted by release system geometry corrections
• → adjusting release nozzle diameter: 3 cm → 2.5 cm
• Mass flow rate: 4.0 kg/s
9
D30 ... 5,0633
D27 ... 4,4691
D25 ... 4,0081
D24 ... 3,6433
D22 ... 3,2702
0,0
0,5
1,0
1,5
2,0
2,5
3,0
0,0 0,2 0,4 0,6 0,8 1,0 1,2 1,4 1,6 1,8 2,0
Cu
mu
lati
ve
co
riu
m m
ass
[k
g]
Time [s]
D30
D27
D25
D24
D22
KS1
3
3,5
4
4,5
5
5,5
2,2 2,4 2,6 2,8 3M
ass
flo
w r
ate
[k
g/s
]Nozzle diameter [cm]
Mass flow rate
Experimental
boundaries
Mass flow rate 4.0 kg/s at
2.5 cm nozzle diameter
ERMSAR 2017, Warsaw, May 16-18, 2017
Premixing Modelling – Melt Jet Release
• Jet impact velocity
• May be controlled by release system height adjustments
• Simulations in good agreement with analytical solution
• Experimental height 1.9 m gives 3.8 m/s impact velocity
• Not changed
• Jet fragmentation length
• MC3D global jet fragmentation model - fragmentation rate
coefficient (FR)
• FR = 0.075 m3/m2/s (default)
• Jet breakup length: 28 cm
corresponds to X–ray data results
• FR kept default
10
3,1
3,2
3,3
3,4
3,5
3,6
3,7
3,8
3,9
4
1,65 1,70 1,75 1,80 1,85 1,90 1,95
Imp
act
ve
loci
ty[m
/s]
Release height [m]
Simulation impact velocity
Analytical solution
5
10
15
20
25
30
35
0,05 0,1 0,15 0,2 0,25 0,3
Jet
bre
aku
p le
ng
th [
cm]
Fragmentation rate [m3/m2/s]
D = 3 cm
D = 2.5 cm
3,1
3,2
3,3
3,4
3,5
3,6
3,7
3,8
3,9
4
1,65 1,70 1,75 1,80 1,85 1,90 1,95
Imp
act
ve
loci
ty[m
/s]
Release height [m]
Simulation impact velocity
Analytical solution
5
10
15
20
25
30
35
0,05 0,1 0,15 0,2 0,25 0,3
Jet
bre
aku
p le
ng
th [
cm]
Fragmentation rate [m3/m2/s]
D = 3 cm
D = 2.5 cm
ERMSAR 2017, Warsaw, May 16-18, 2017
Comparison with Experimental Data
11
• Melt jet propagation
Initial good agreement, but ovepredicted melt
penetration in simulation after full jet breakup
Melt bottom contact: Sim 0.86 s, Exp 1.18 s
• Void fraction evolution
Global (full line) and within X-ray
window (dashed line)
Similar void fraction development,
but shifted (delayed) in simulation
0,0
0,2
0,4
0,6
0,8
1,0
1,2
1,4
1,6
1,8
2,0
-0,2 0,0 0,2 0,4 0,6 0,8 1,0 1,2 1,4 1,6 1,8 2,0
Fro
nt
jet
po
siti
on
[m
]
Time [s]
Experiment
Melt Front
water height at 1.15 m
0
0,1
0,2
0,3
0,4
0,5
0,6
0,7
0,0 0,2 0,4 0,6 0,8 1,0 1,2 1,4 1,6 1,8 2,0
Void
frac
tio
n
Time [s]
Exp. Total
Exp. Frame
Sim. Total
Sim. Frame
ERMSAR 2017, Warsaw, May 16-18, 2017
Comparison with Experimental Data
• Lateral premixture extension
• Defined as radius inside which 80% of void in each horizontal slice is present
12
initial water level
0,745
1,045
0 0,1
KS-4 test (extension yellow curve) Simulation (extension blue curve)
• Results presented at time of MBC (similar premixture state but not same time)
• Not very reasonable to compare such complex phenomena based on a single snapshot in a time → averages